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Date:   Tue, 28 Apr 2020 01:02:10 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     peng.fan@nxp.com
Cc:     konrad.wilk@oracle.com, boris.ostrovsky@oracle.com,
        jgross@suse.com, sstabellini@kernel.org,
        xen-devel@lists.xenproject.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-imx@nxp.com
Subject: Re: [PATCH] xen/swiotlb: correct the check for
 xen_destroy_contiguous_region
Message-ID: <20200428080210.GA25643@infradead.org>
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On Tue, Apr 28, 2020 at 03:33:45PM +0800, peng.fan@nxp.com wrote:
> 
> In xen_swiotlb_alloc_coherent, if !(dev_addr + size - 1 <= dma_mask) or
> range_straddles_page_boundary(phys, size) are true, it will
> create contiguous region. So when free, we need to free contiguous
> region use upper check condition.
> 
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
>  drivers/xen/swiotlb-xen.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index b6d27762c6f8..ab96e468584f 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -346,8 +346,8 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>  	/* Convert the size to actually allocated. */
>  	size = 1UL << (order + XEN_PAGE_SHIFT);
>  
> -	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
> -		     range_straddles_page_boundary(phys, size)) &&
> +	if (((dev_addr + size - 1 > dma_mask) ||
> +	    range_straddles_page_boundary(phys, size)) &&
>  	    TestClearPageXenRemapped(virt_to_page(vaddr)))

No need for the inner braces.

But more importantly please factor our a helper that can be used by
alloc and free to make sure that they always stay in sync.  Something
like:

static inline bool xen_swiotlb_need_contiguous_region(struct device *dev,
		phys_addr_t phys, size_t size)
{
	
	return xen_phys_to_bus(phys) + size - 1 > dev->coherent_dma_mask ||
		range_straddles_page_boundary(phys, size))
}